Multi-focal contact lens

ABSTRACT

A tool for forming a soft contact lens having an optical zone formed with a center spherical surface and surrounding aspheric surfaces is disclosed. The tool includes a lens holder having a perfectly centered rearwardly extending cylindrical portion received in a collet of a lens cutting lathe and a transverse front end wall defining a front end opening receiving the lens blank body projecting forwardly through the opening. The lens blank is formed with a mounting flange seated against a rear facing step in the transverse end wall. The lens body is retained in the holder with an insert threadedly received in the holder. A set screw received in the insert applies pressure to the lens blank rear surface to deform the front concave surface which has been previously cut and polished to a spherical surface. The deformed front concave surface is re-cut into spherical shape in at least preselected portions of the front surface so that, upon release of squeezing pressure, the preselected portions of the front surface are aspheric to define portions of the optical zone having continuously variable optical powers. The center of the optical zone preferably remains spherical for improved night vision.

TECHNICAL FIELD

The present invention relates generally to contact lenses and, moreparticularly, to multi-focal soft contact lens and apparatus for cuttingthe opposing surfaces of a contact lens blank on a lens cutting lathe.

BACKGROUND ART

Bifocal contact lens having an optical zone defined by an asphericposterior curve and a spherical anterior curve are known. The asphericback curve portion has a controlled degree of change so that, within apredetermined power range, light rays from objects at all distancesfocus directly on a common focal point. When placed on a human cornea,this contact lens acts as a refractive medium to focus light rays backupon the retina.

The above lens is a multi-focal design with the spherical front curvedirectly relating to the aspheric optical zone back curve. However,since the aspherical back curve entirely dominates the optical zone,distance night vision becomes impaired. This is because when the eyepupil dilates at night it no longer predominantly receives light throughthe center region of the lens and instead tends to pick up light furtherinto the aspheric part of the lens which is normally used for nearvision.

It is accordingly one object of the present invention to provide acontact lens having aspherical curve characteristics to maintain theadvantage of a multi-focal design while providing curvaturecharacteristics, within the optical zone portion of the lens, whichimproves night vision.

Another object of the invention is to improve night vision by providinga distant vision zone in the center of the optical zone, in the form ofa spherical base curve.

Still another object is to provide the foregoing curvaturecharacteristics in a multi-focal soft contact lens.

FIG. 1 is an illustration of a tool 10 used for cutting an asphericposterior curve in a pre-cut and polished lens blank 12. Tool 10comprises a lens holder 14 having a cylindrical sidewall 16 formed withinternal threads 17 and a transverse front end wall 18 having a centralopening 19 receiving the pre-cut lens blank 12 therein. The lens blankbody 12 has a diameter corresponding to the diameter of the front endwall opening 19 through which it extends. The lens blank body 12 isformed with an annular flange 20 of a larger diameter which is receivedagainst the rear facing surface 22 of the end wall 18 in seating contactthereagainst. A cylindrical retainer 24 having an external thread 25along its cylindrical sidewall has a central depression 26 in itstransverse front end receiving a ball 27 adapted to apply pressure tothe center of the lens blank body 12 upon threading of the retainer intothe lens holder. In such threaded contact, a radial set screw 28extending through the cylindrical sidewall 16 of the lens blank holder14 is rotated to contact and apply a radial tightening pressure to theretainer 24 to tighten the parts 14,24 together. The rear end of theretainer is formed with a rearwardly extending cylindrical extension 29adapted to be received in the chuck of a lathe in preparation forcutting the front facing surface of the lens blank 12 projecting fromthe mounting tool 10.

There are a number of problems associated with the prior art device ofFIG. 1. For example, once a desired amount of pressure was exertedagainst the lens 12 by the ball 27, tightening of the set screw 28 toclamp the two pieces 14,24 together tended to shift the cutting axis Cof the lens blank in relation to the mounting axis M of the retainer inthe collet or chuck. This misalignment tended to cause the lens to becut off-center. Notwithstanding possible misalignment caused bytightening of the parts 14,24 together with a radial set screw 28, therealso existed a tendency for the lens not to run perfectly true in thelathe by virtue of the two part construction wherein the mounting axis Mwas formed in one part 24 while the cutting axis C was formed in thefront or lens blank holder part 14. In other words, the inherent natureof the two-part construction required extremely precise machiningtolerances to enable proper alignment of the cutting axis C with themounting axis M.

It is another object of the present invention to provide a tool forcutting a contact lens wherein the cutting axis is properly aligned witha collet mounting axis of the tool.

Yet another object is to provide a tool for producing a desireddistortion in a lens blank body in controlled, easily measured amounts.

Yet another object is to be able to distort the lens blank to permitformation of aspheric surfaces therein in preselected areas of the lensblank.

Another object is to permit distortion of the lens blank in certainareas of the concave surface without distorting other preselected areasof the concave surface to permit the formation of aspheric and sphericsurfaces in the lens blank.

Yet another object is to provide a tool for cutting a lens blank whereinthe lens cutting axis and the mounting axis are formed in the samecomponent of the tool.

SUMMARY OF THE INVENTION

A multi-focal contact lens, in accordance with the present invention,comprises a lens body having a concave surface and a convex surface witha central optical zone portion confined to the center part of the lens.The optical zone portion includes a spherical curve in the center regionof the concave surface and an aspheric curve which surrounds the centerspherical region. The center spherical region formed in a predeterminedcenter portion of the optical zone advantageously improves distancenight vision by providing a spherical center in the optical zone throughwhich the eye sees far distant objects, compensating for the expansionof the eye pupil at night into radially distant areas of the asphericcurve having greater aspheric curvature for near vision and lesscurvature of the aspheric curve closer to the central spherical region.

The concave surface may be formed with a carrier portion extending fromthe periphery of the optical zone out to the edge of the lens. Thecarrier portion is preferably spherical to control the manner in whichthe lens edge lifts from the eye and so that oxygen and tears canproperly flow under the lens.

The multi-focal contact lens is a soft contact. The spherical curve inthe center region of the optical zone portion has a substantiallyconstant optical power adapted to create a predominant far vision imagefor improved night vision while the aspheric curve surrounding it has acontinuous varying optical power as a function of radial distance fromthe center. The center spherical region preferably has a diameter ofapproximately 2-4 mm and the aspheric curve begins at the periphery ofthe spheric curve to extend radially outwardly therefrom. The peripheralsurface is essentially spherical.

A tool for forming a contact lens from a lens blank body having frontand rear surfaces and a side surface formed with a mounting flange, inaccordance with the present invention, comprises a lens holder beingopen at opposite ends thereof to receive the lens blank body through therear end opening and to enable the concave surface of the lens blankbody to be exposed to a cutting device from the front end opening of theholder. The mounting flange is in seating contact with a rear facingportion of the front end wall surrounding the opening. An insert,mounted in the lens holder, has a front end wall for contacting theperiphery of the lens blank body (i.e., the flange thereby beingsandwiched between the seat of the front end wall and the insert) toretain the body in the front end opening. A distortion force applyingmeans, mounted within the retainer, applies a force to a rear surface ofthe lens blank body which distorts the curvature of the concave surface.

The lens holder is preferably a hollow cylindrical body having arearwardly extending outer cylindrical surface which is perfectlycentered with the longitudinal axis of the holder. The outer surface isadapted to be received in a conventional collet for securing the holderand thereby the lens in a known lens cutting lathe. The hollowcylindrical body thereby defines the mounting axis. The front endportion of the lens holder, located forwardly of the outer cylindricalsurface, is formed with the transverse front end wall and front endopening within the wall. The cylindrical edge subtending the openingcontacts the outer cylindrical surface of the lens blank in centeringengagement to thereby align the cutting axis of the lens blank with themounting axis of the lens holder by providing appropriately centeredsurfaces machined into the same lens holder body.

An interior thread is formed in the hollow cylindrical body of the lensholder rearwardly of the transverse front end wall. The retainer is asubstantially cylindrical member having an exterior thread engaging theinterior thread of the lens holder. The front end face of thecylindrical container is adapted to face and loosely contact the rearsurface of the lens blank body to thereby act as a rear stop retainingthe lens blank within the front end opening, in cooperation with therear facing surface of the transverse front end wall acting as a frontstop. The front and rear stop arrangement advantageously locates thelens blank within the front end opening without applying a force to thelens rear surface which would distort the lens concave surface.

The distortion force applying means is preferably a set screw extendingthrough the center of the insert, in threaded engagement therewith, tocontact the center portion of the lens blank body rear surface. The setscrew may have an exterior thread engaging a threaded central boreextending through the insert. The front end face of the set screw whichis adapted to contact the lens blank rear surface has a centraldepression defined by a surrounding edge in the front end face. Thisedge establishes points of contact (or a continuous line of contact)with the lens blank rear surface, the locus of the points of contactdescribing a circle preferably being a circular line of pressure pointscontinuously radially spaced from the center of the lens blank rearsurface. The depression in the front end face of the set screw may beconical, semispherical, etc., and the continuous edge defining thepoints of contact is preferably a rounded edge in cross-section toprevent cutting into or cracking of the lens blank.

A method of fabricating a multi-focal contact lens from a cylindricallens blank having two opposed surfaces comprises the steps of cuttingand polishing one of the opposing surfaces to a concave spherical shapeand squeezing the lens blank to deflect and deform at least part of thespherical surface by a controlled amount. At least preselected portionsof the polished deformed surface are then re-cut to a desired concavespherical surface so that upon release of the deforming pressure thesaid desired concave spherical surface becomes an aspheric concavesurface in the preselected portions. The other opposed surface of thelens blank is then finished to form a convex surface of the lens.

In accordance with a preferred feature of the invention, a centerportion of the concave surface is not re-cut so that upon release ofdeforming pressure the center portion of the lens remains spherical withan aspheric curve surrounding it. The center spherical surface and thesurrounding aspheric surface are within the optical zone portion of thelens.

The concave surface may also be formed with a carrier portion extendingfrom the periphery of the optical zone out to the edge of the lens. Thecarrier portion is preferably defined by a spherical curve.

The spherical curve in the center region of the optical zone portion hasa substantially constant optical power adapted to create a predominantfar vision image for improved night vision while the aspheric curvesurrounding the center spherical region is of continuous varying opticalpower.

The center spherical region preferably has a diameter of approximately2-4 mm and the aspheric curve begins at the periphery of the sphericcurve to extend radially outwardly therefrom.

The lens is squeezed by applying pressure against the other opposed(e.g., rear) surface to deflect, by distortion, the opposed (e.g.,front) concave surface which has been pre-cut to spherical shape. Thepressure is preferably applied through a plurality or continuous line ofcontact points surrounding the center of the other surface. The pluralcontact points preferably define a continuous circular line of forcewhere the points of pressure are equi-spaced from the lens center. Thisapplication of pressure will not result in distortion of the sphericalcenter region of the opposed surface during squeezing. In the event thatpressure is applied to the center of the other opposed surface duringsqueezing, which deforms the center portion of the opposed surface aswell as the surrounding portions thereof, the spherical center portionmay nonetheless be maintained by limiting the re-cutting process tothose areas outside the center portion in which spherocity is desired tobe maintained.

Still other objects and advantages of the present invention will becomereadily apparent to those skilled in this art from the followingdetailed description, wherein only the preferred embodiments of theinvention are shown and described, simply by way of illustration of thebest mode contemplated of carrying out the invention. As will berealized, the invention is capable of other and different embodiments,and its several details are capable of modifications in various obviousrespects, all without departing from the invention. Accordingly, thedrawing and description are to be regarded as illustrative in nature,and not as restrictive.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an exploded sectional view of a prior art tool for mounting alens blank body to a lathe;

FIG. 2 is an exploded sectional view of a tool for mounting a lens blankto a lathe in accordance with the present invention;

FIG. 2A is a magnified view of a part of the tool of FIG. 2;

FIG. 2B is a sectional view of the tool parts in assembled relation;

FIG. 3 is a sectional view of a soft contact lens manufactured inaccordance with the present invention; and

FIG. 4 is a plan view of the lens of FIG. 3, wherein all coordinates ofFIGS. 3 and 4 are given wet.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to FIGS. 2-4, a tool 30 for deforming and shaping a lensblank L in accordance with the method of the invention is depicted. Theblank L is of a type from which soft contact lenses are typicallyformed. The blank L is disc-shaped and usually provided with parallelopposed surfaces 32 and 34 in which one surface is pre-cut and polishedto a spherical surface 32 while the rear or other surface 34 remainsflat and therefore initially uncut. A flange 36, coplanar with the flatrear surface 34, is cut into the sidewall of the blank for mounting theblank to the tool 10 in the unique manner described infra.

The tool is of a three-part construction comprised of a lens blankholder 40 formed with a hollow cylindrical body portion 42 open at therear end 42a thereof and a transverse end wall 44 defining a front endopening 46 of the tool 10 through which the front surface 32 of the lensblank L projects. The inner diameter of the hollow cylindrical portion42 is greater than the outer diameter of the lens blank flange 36 whilethe diameter of the front end opening 46 corresponds to the diameter ofthe lens blank sidewall projecting upwardly from the flange. Thecircular edge defining the front end opening 46 in the transverse frontwall 44 defines a cutting axis C' adapted to extend through thegeometric center of the lens blank L. The exterior cylindrical surface48 of the hollow cylindrical body portion 42 is adapted to be receivedin a conventional collet (not shown). This exterior surface 48 defines amounting axis M' of the tool which is perfectly aligned with the cuttingaxis C'.

The feature of forming the lens blank holder 40 with an exteriorcylindrical surface 48 defining the mounting axis M' and with atransverse front wall 44 having an opening 46 defining the cutting axisC' greatly improves accuracy in cutting the lens blank by facilitatingthe manufacture of the cylindrical retainer to precise and close machinetolerances within the same manufactured piece.

The pre-cut and polished lens blank L is retained in the front endopening 46 of the lens blank holder 40 with a retainer insert 50 whichis a cylindrical body having an exterior diameter generallycorresponding to the interior diameter of the hollow cylindrical body 42of the holder. The retainer insert 50 is formed with an exterior thread52 adapted to be threaded to an interior thread 49 formed in the lensholder body 40. In the threaded position of FIG. 2B, the front end face54 of the retainer 50 insert loosely contacts the back surface 34 of thelens blank L including the flange 36. The flange 36 is now sandwichedbetween the front end transverse wall 44 of the lens holder (front stop)40 and the front end wall 54 of the retainer insert (rear stop) 50. Itis to be understood that the retainer insert 50 does not exert anysignificant pressure against the rear surface 34 of the lens blank Lsufficient to distort the lens blank concave surface 32. The retainerinsert 50 is provided merely to mount the lens blank body L in the frontend opening 46 with the lens blank front surface 32 extending forwardlyof the opening as depicted in FIG. 2.

In accordance with the invention, the pre-cut and polished sphericalconcave surface 32 of the lens blank L is deformed into an asphericsurface, prior to recutting, by means of a set screw 60 extendingthrough a central bore 56 in the retainer insert 50 to contact the lensblank rear surface 34 and thereby distort by "squeezing" the concavefront surface 32 into an aspheric curvature. While squeezed, the concavesurface 32 of the lens blank L is cut on the lathe. The cut and polishedfront surface (spherical before deformation), before releasing and whiledeformed is aspherical, is re-cut in selected parts back to spherical,and, after release, the selected re-cut parts of the front surfacebecome aspherical. The amount of deformation created by the squeeze ismeasured with a conventional radiuscope (not shown) which indicates theamount of displacement of curvature from the spherical curve. Afterinducing the desired amount of deflection as measured on the radiuscope,the concave surface 32 is then re-cut using conventional techniques.

In accordance with a unique feature of the invention, the front end 62of the pressure applying set screw 60 is formed with a centraldepression 64 which may be a conical depression as depicted in FIG. 2 ora semi-spherical depression 64a as depicted in FIG. 2A. A circular ridge65 defined by the depression 64 and 64a and sidewall 66 of the set screw60 is adapted to contact the lens blank rear surface 34 to deform thelens concave surface 32 from spherical to aspherical curvature asmentioned above. The deflection transmitted from the rear to frontsurface of the lens L is greatest along a locus formed by theintersection of the concave front surface 32 with an imaginary cylinderformed by projecting the circular line of force (i.e., points of contact65 between the set screw 60 and the lens rear surface 34) toward thefront surface. Since no pressure is applied to the lens rear surface bythe central depression 64, it will be appreciated that the sphericalcentral portion of the lens front surface (i.e., overlying thedepression) is not rendered aspherical during distortion or squeezing ofthe blank. Thereby, when re-cutting the lens concave surface (which is aspherical surface which becomes aspherical during squeezing) to aspherical curve, it will be appreciated that the cut and polished frontsurface after releasing becomes aspherical from the locus of pointsundergoing greatest deflection as mentioned above to a desired radiallyoutward extent up to the peripheral edge of the front surface itdesired.

As depicted in FIG. 2A, the front edge 65 of the set screw which appliesthe deforming pressure to the lens front surface by contact with therear surface, is a rounded edge which is semi-spherical in cross-sectionso as to avoid cutting into the lens. Alternatively, the front edge maybe a flat edge less than approximately 1 mm in width. If desired, theset screw 60 may carry a spherical ball (not shown) projecting forwardlyfrom the depression 64 to contact the center of the lens rear surface(i.e., ball to rear surface contact as depicted in FIG. 1).

When cutting the lens blank L on a lathe up to the center of the lensfront surface while squeezing the lens, it is possible to render theentire optical zone of the lens into an aspheric condition such asdepicted in U.S. Pat. No. 4,580,882 to Nuchman et al or as obtained witha lens cut on the prior art tool of FIG. 1. As a preferred feature ofthe present invention, however, the set screw is utilized without theball so that deforming pressure is applied only to the lens blank rearsurface by the circular edge 65 surrounding the depression 64. In thismanner, the central portion of the optical zone (the central portioncorresponding to the diameter of the depression in the set screw)advantageously remains a spherical surface both during and after releaseof the squeezing pressure while the surrounding portions of the opticalzone are aspheric.

By providing a spherical curve in the center portion 70 of the opticalzone 72 (the center portion being 2-5 mm and preferably 2-4 mm with anoptical zone of 7-9 mm in diameter) as depicted in FIGS. 3 and 4, thespherical curve in the center portion of the optical zone provides theeye with a viewing area for distance night vision. This is advantageoussince, when the eye pupils expand at night, there is a tendency for theeye to pick up further into the aspheric parts of the lens locatedradially outward from the center portion which tends to cut down ondistance night vision due to the greater aspherocity in the radiallyoutward portions of the optical zone. By providing a spheric curve inthe center portion, however, this problem is effectively eliminatedsince the pupil can now focus on light rays coming through the centerspherical portion for improved distance night vision.

The peripheral carrier portion 76 of the lens front surface 32 ispreferably a spherical curve. This carrier portion 76 is located outsidethe optical zone portion where spherocity is preferred as a means tocontrol the manner in which the contact lens edge lifts from the eye andso that oxygen and tears can flow under the lens. The spherocity of thecarrier portion 76 can be maintained by limiting the re-cutting of thespherical lens front surface 32 (prior to squeezing) to only thatportion of the optical zone located between the carrier portion 76 andthe center portion 70 discussed above.

The forward end of the sidewall 42 of the lens blank holder 40 is formedwith an annular step 80 that effectively contacts the front of thecollet to properly delimit the depth of the tool within the collet.

The feature of initially cutting and polishing the lens blank concavesurface 32 into a spherical shape enables the lens manufacturer to knowexactly how much deflection to put into the lens via controlling thesqueezing pressure through rotation of the set screw 60 since themanufacturer can precisely read the compressed spherical curve with aradiuscope.

It is an important feature of this invention to limit the extent of thediameter of the spherical center portion 70 of the optical zone 72 toabout 2-4 mm in diameter while retaining an aspheric curve insurrounding portions of the optical zone so as to obtain the benefit ofimproved distance night vision through the center portion of the lenswhile retaining the bifocal or multiple continuous vision effect fromthe lens in the aspheric portion of the optical zone surrounding thecenter portion.

After cutting the concave surface 32 of the lens blank L (which becomesthe rear or posterior surface of the finished contact lens) in themanner set forth above, the lens blank is removed from the tool 30 andthis concave surface is now affixed with dental wax to an additionaltool as known in the art. This additional tool is inserted into thelathe via the collet and the spherical front curve (anterior curve) iscut from rear surface 34 in a known manner to form the front or convexsurface of the lens.

It will be readily seen by one of ordinary skill in the art that thepresent invention fulfills all of the objects set forth above. Afterreading the foregoing specification, one of ordinary skill will be ableto effect various changes, substitutions of equivalents and variousother aspects of the invention as broadly disclosed herein. It istherefore intended that the protection granted hereon be limited only bythe definition contained in the appended claims and equivalents thereof.

I claim:
 1. A multi-focal contact lens, comprising:a lens body having a concave surface and a convex surface and a central optical zone portion confined to the center part of the lens, said optical zone portion including a spherical curve in the center region of the concave surface and an aspheric curve in the concave surface which surrounds the center spherical region, wherein said spherical curve and aspheric curve and regions surrounding the optical zone have continuous measurable power at any part on the lens.
 2. The lens of claim 1, wherein said concave surface is formed with a carrier portion extending from the periphery of the optical zone out to the edge of the lens, said carrier portion being defined by a spherical curve.
 3. The lens of claim 2, wherein said multi-focal contact lens is a soft contact lens.
 4. The lens of claim 2, wherein said spherical curve in the center region of the optical zone portion has a substantially constant optical power adapted to create a predominant far vision image for improved night vision while the aspherical curve surrounding the center spherical region has a continuous varying optical power.
 5. The lens of claim 4, wherein said center spherical region has a diameter of approximately 2-5 mm.
 6. The lens of claim 5, wherein said center spherical region has a diameter of approximately 2-4 mm and the aspheric curve begins at the periphery of the spheric curve to extend radially outwardly therefrom.
 7. The lens of claim 6, wherein the convex surface is substantially spherical. 